As is well known to those skilled in the art, as industrialization has advanced in certain areas, the usage of various resources has rapidly increased. In particular, the production and supply of resources such as oil has arisen as a very important issue. For this reason, drill ships equipped with drilling equipment and FPSO (Floating, Production, Storage and Offloading) units which are floating vessels used by the offshore industry were recently developed and have been used in investigation and drilling work to produce various resources from the deep sea.
In vessels such as drill ships or the like, a moon pool, which is a comparatively large opening, is formed through a central portion of a hull so that drilling pipes or mining pipes are moved to the bottom of the sea through the moon pool. The moon pool is indispensable for such functions as drilling for example, but becomes a weak point in terms of the anchoring of the ship, the voyage stability and the ship's propulsion performance.
In particular, in a conventional drill ship, due to a sloshing phenomenon which is induced by relative movement between seawater in the moon pool and seawater outside the ship, when the drill ship runs, resistance to the ship is increased so that the velocity thereof is reduced. In addition, power consumption increases, resulting in increased fuel consumption. Furthermore, if the ship runs on art area of pack ice, the pack ice may enter the hull of the ship through the moon pool, thus causing the problem of damage to the hull.
In an effort to overcome these problems, such as an increase of resistance attributable to the motion of seawater in the moon pool, a technique was proposed in which a door structure or flap structure is used to completely close the moon pool when necessary. However, in the terms of the structure for completely closing the moon pool, the weight of the ship is excessively increased. Therefore, there are many difficulties in operating equipment such as tugboats for tugging the heavy ship.